1) Field of the Invention
This invention relates to an emulsion fuel engine which uses an emulsion fuel as a fuel.
2) Description of the Related Art
To produce less exhaust gas and reduce the specific fuel consumption, diesel engines using an emulsion fuel are known. The term "emulsion fuel" as used herein means a fuel formed by emulsifying mutually-insoluble fuels, for example, water and diesel fuel, water and heavy oil, or methanol and diesel fuel.
Referring to FIG. 10, the construction of a conventional emulsion fuel engine will be described. The conventional emulsion fuel engine shown includes a fuel tank 1 in which an emulsion fuel (for example, water and diesel fuel) is stored. Arranged between the fuel tank 1 and an injection pump 2 is a fuel pipe FP which is provided with a fuel pump 3 for delivering the emulsion fuel and also with a fuel filter 4.
The injection pump 2 is provided with a reciprocating plunger 7 which moves up and down as a camshaft 5 rotates together with a cam 6. The injection pump 2 begins to draw the fuel after an upper end face of the plunger 7 has come to a position lower than a fuel draw/spill port 9. After the upper end face of the plunger 7 has moved to a position above the fuel draw/spill port 9, the injection pump 2 begins to deliver the fuel under pressure. When a lead 10 formed in a peripheral wall of the plunger 7 has overlapped the fuel draw/spill port 9, the injection pump 2 terminates the delivery of the fuel under pressure. Designated at numeral 11 is a delivery valve for the prevention of a reverse flow.
An injection pipe IP is arranged between a top portion of the injection pump 2 and an injection nozzle 12. A fuel feed channel 13 is formed inside the injection nozzle 12. Through the fuel feed channel 13, the fuel which has been delivered under pressure from the injection pipe IP is guided to a lower part of the nozzle 12. A needle valve 14 is lifted by the pressure of the fuel, whereby the fuel is injected into the combustion chamber through injector holes 15.
The fuel discharged from the injection pump 2 and the injection nozzle 12 is returned to the fuel tank 1 via a fuel return pipe 16.
In the conventional emulsion fuel engine, an emulsion fuel prepared in advance is merely stored in the fuel tank 1 instead of diesel fuel.
Further, when the emulsion fuel is left for a long time in the fuel tank 1, the diesel fuel and the water are separated from each other, and consequently, water is sometimes injected upon next starting of the engine, resulting in the problem that the conventional emulsion fuel engine is low in ignition performance and sometimes suffers from failure in starting.
A diesel engine injection system includes many parts operating in the fuel with micron-level clearances. An emulsion fuel with enclosed water droplet induces excess wear due to insufficient lubrication and rusting at the injection pump 2, resulting in the problem that the durability of the injection pump 2 is reduced.
At the injection nozzle 12, the injector holes 15 may be clogged by abraded particles formed by the excessive wear, leading to the problem that the durability of the injection nozzle 12 is reduced.
An apparatus is already known and disclosed, for example, in U.S. Pat. No. 3,933,132 wherein water or non-aqueous liquid is introduced to an arbitrary position between a delivery valve and a fuel injection nozzle and then the water or non-aqueous liquid is introduced into an injection pipe by a negative pressure produced by a fuel drawing back action of the delivery valve.
With the prior art apparatus, however, since only water or non-aqueous liquid is introduced directly into the injection pipe and then injected from the injection pipe together with fuel, the fuel and the water or non-aqueous liquid are not compulsorily mixed with each other but remain in a naturally mixed condition. As a result, it sometimes occurs that the fuel and the water or non-aqueous liquid are not mixed uniformly and only the water or non-aqueous liquid is injected by a large amount while the fuel is injected but by a small amount. In this case, the combustion itself may not be established and the original effect of reduction of NOx by use of the emulsion fuel cannot be anticipated sufficiently.
Another apparatus is also known and disclosed, for example, in Japanese Utility Model Laid-Open Application No. 56-142243 wherein such an auxiliary fuel as water or non-aqueous liquid as described above is not drawn in by a negative pressure caused by a drawing back action of a delivery valve but is fed under pressure and introduced to an arbitrary position from the delivery valve to injector holes of a fuel injection nozzle while adjusting the pressure of the auxiliary fuel in response to an operating condition of the engine by means of a pressure regulator.
The prior art apparatus is improved comparing with the apparatus disclosed in U.S. Pat. No. 3,933,132 in that the auxiliary fuel pressure can be adjusted in response to an operating condition of the engine. However, the apparatus still has similar subjects to those of the other apparatus described hereinabove.